This invention relates to the field of pacemakers and pacing algorithms; and, in particular, to delivering atrial overdrive pacing to an atrium to decrease the recurrence of atrial fibrillation after the delivery of a therapy to terminate an atrial arrhythmia.
Atrial fibrillation is probably the most common form of cardiac arrhythmia. Patients afflicted with atrial fibrillation generally experience rapid and irregular heartbeats and may even experience dizziness as a result of reduced cardiac output. Atrial fibrillation occurs suddenly and can be corrected by an electrical shock into the atria of the heart. Implantable atrial defibrillators detect the presence of atrial fibrillation and provide a single cardioverting pulse of electrical energy (or electrical shock) as the therapy. However, atrial fibrillation usually returns within minutes after delivery of the electrical therapy in about one-half of the patients with atrial fibrillation episodes.
One mechanism for preventing atrial fibrillation involves providing atrial overdrive pacing therapy. This type of therapy paces the right atrium at a rate faster than the atrial intrinsic rate for a predetermined period of time. The implanted device applies pacing pulses to the right atrium (referred to as xe2x80x9cA pulsesxe2x80x9d) at a time in the cardiac cycle that is just prior to the occurrence of a spontaneous atrial depolarization (referred to as a xe2x80x9cP-wavexe2x80x9d). Thus, in overdrive pacing, a sequence of A-pulses applied to the atrium causes the atrium to depolarize at a time in the cardiac cycle that is slightly before the spontaneous occurrence of the P-wave, thereby preventing the on-set of an atrial fibrillation episode.
During preventative atrial overdrive pacing, the ventricular rate of a patient may drop to an extremely low level. Thus, most implanted devices switch to a dual chamber pacing and sensing mode (DDI mode) and thereafter determine whether the on-set of atrial fibrillation was prevented. After a predetermined time of pacing in DDI mode, a normal pacing mode wherein the atria and ventricles are synchronized (DDD mode) is resumed. For a more detailed discussion and definition of the various pacing and sensing mode codes for implantable medical devices, reference is made to The NASPE/BPEG Generic Pacemaker Code for Antibradyarrhythmia and Adaptive-Rate Pacing and Antitachyarrhythmia Devices, by Bernstein, et.al., (NASPE in July, 1987), which is incorporated herein by reference.
The above approach presents several problems. First, when sustained high-rate atrial tachyarrhythmias are present, pacing in DDI mode can result in excessive high-rate ventricular pacing. This, in turn, causes patient discomfort, increases manifestations of heart failure symptoms, and may induce atrium or ventricular arrhythmias. Moreover, traditional pacing devices limit the pacing rate available in DDI mode such that rates are insufficient for overdrive pacing during high-rate atrial arrhythmias.
What is needed, therefore, is an improved system and method for preventing atrial fibrillation. The system is adapted to prevent re-occurrence of atrial fibrillation following shock delivery. Ideally, the therapy should take effect quickly and without an associated increase in ventricular pacing rates.
Various embodiments of the present invention are directed to addressing the above and other needs in connection with preventing early recurrence of atrial fibrillation by pacing a heart in an atrial overdrive mode for a selected period of time immediately after applying an electrical cardioverting therapy.
According to one embodiment of the invention, a system is provided for preventing the early reoccurrence of atrial fibrillation (ERAF) following cardioversion, defibrillation, or anti-tachy pacing (ATP) therapy in the atrium. After the delivery of such therapy, the device switches to a DDI mode for a predetermined number of cycles, which, in the preferred embodiment, is only a single cycle. This switch to DDI mode may occur without any substantial delivery following therapy delivery. Another mode switch then occurs to an AAI pacing mode with backup VVI pacing in the ventricle.
In one embodiment of the invention, a method of preventing ERAF is provided. The method includes utilizing an implanted medical device (IMD) to apply an ATP or high-voltage shock therapy to the atrium. Thereafter, the implanted medical device paces the heart with an atrial overdrive pacing therapy with backup ventricular pacing. Prior to this mode switch, one or more optional pacing cycles may be performed in DDI mode.
According to one aspect of the invention, atrial overdrive pacing with VVI backup may be performed for a user-selectable time and pacing rate. The rate may also optionally decrease over time so that the system reverts to a normal pacing rate in DDD mode after the predetermined time.
Yet another aspect of the invention involves terminating atrial overdrive pacing after a reoccurrence of atrial fibrillation is detected. Thereafter, appropriate therapy may be delivered, including ATP or high-voltage shock therapy. Additional aspects of the invention will be apparent to those skilled in the art from the following description and accompanying drawings.